System and method for automatic control of exposure time in an imaging instrument

Abstract

In an embodiment, a computer-implemented method of calibrating an imaging system in real-time, comprising: obtaining a first reading by a first sensor; establishing a dynamic link between the first reading and exposure time of a second sensor; using the dynamic link to control the exposure time of the second sensor; obtaining a second reading by the second sensor during the controlled exposure time; wherein the steps are performed by one or more computing devices.

What is claimed is: 
     
       1. A computer-implemented method of calibrating an imaging system in real-time, comprising:
 under control of stored program instructions executed using a processor, obtaining a first reading by a first sensor; 
 after the first reading by the first sensor is obtained, establishing, by executing the instructions, a dynamic link expressing a proportional relationship between the first reading and exposure time of a second sensor; 
 by executing the instructions, using the dynamic link to calibrate the exposure time of the second sensor; 
 by executing the instructions, obtaining a second reading by the second sensor during the calibrated exposure time; 
 wherein the method is performed by one or more computing devices. 
 
     
     
       2. The computer-implemented method of  claim 1 , wherein the obtaining the first reading, the establishing, the using, and the obtaining the second reading are performed using a processor of an unmanned aircraft system (UAS) during one UAS mission. 
     
     
       3. The computer-implemented method of  claim 2 , wherein the obtaining the first reading includes:
 obtaining solar irradiance (E sun min ) for a given wavelength at the lowest elevation angle allowed by a light diffuser of the first sensor; 
 obtaining solar irradiance (E Sun max ) for the given wavelength at the maximum elevation angle of the UAS mission; 
 calibrating exposure time of the first sensor to capture readings between E Sun min  and E Sun max ; 
 transforming the first reading into an observed solar irradiance E Sun obs . 
 
     
     
       4. The computer-implemented method of  claim 3 , wherein the establishing includes:
 determining, based on E Sun obs , the maximum radiance value (L Detector max ) of an array of light detectors of the second sensor; 
 determining, based on L Detector max , the maximum irradiance value (E Detector max ) of an array of light detectors of the second sensor. 
 
     
     
       5. The computer-implemented method of  claim 4 , wherein the dynamic link is a proportion between E Sun obs  and E Detector max . 
     
     
       6. The computer-implemented method of  claim 5 , wherein the using includes applying the proportion as a scale to a nominal exposure time of the second sensor. 
     
     
       7. The computer-implemented method of  claim 5 , wherein the dynamic link includes a factor. 
     
     
       8. The computer-implemented method of  claim 7 , wherein the factor is maximum reflectivity of a target (ρ Max target ). 
     
     
       9. The computer-implemented method of  claim 1 , wherein the imaging system is coupled with an unmanned aircraft system (UAS). 
     
     
       10. The computer-implemented method of  claim 9 , wherein the first sensor is an upwards looking sensor on the UAS and the second sensor is a downwards looking sensor on the UAS. 
     
     
       11. An imaging system comprising:
 a first sensor, a second sensor, and a system control board all communicatively coupled together; 
 wherein the first sensor is configured to obtain a first reading; 
 wherein the system control board is configured to:
 after the first reading by the first sensor is obtained, establishing a dynamic link expressing a dynamic relationship between the first reading and an exposure time of the second sensor; 
 use the dynamic link to calibrate the exposure time of the second sensor; 
 
 wherein the second sensor is configured to obtain a second reading during the calibrated exposure time. 
 
     
     
       12. The imaging system of  claim 11 , wherein communication between the first sensor, the second sensor, and the system control board is provided in real-time during one unmanned aircraft system (UAS) mission. 
     
     
       13. The imaging system of  claim 12 , wherein the first reading is obtained by:
 obtaining solar irradiance (E Sun min ) for a given wavelength at the lowest elevation angle allowed by a light diffuser of the first sensor; 
 obtaining solar irradiance (E Sun max ) for the given wavelength at the maximum elevation angle of the UAS mission; 
 calibrating exposure time of the first sensor to capture readings between E Sun min  and E Sun max ; 
 transforming the first reading into an observed solar irradiance E Sun obs . 
 
     
     
       14. The imaging system of  claim 13 , wherein the dynamic link is established by:
 determining, based on E Sun obs , the maximum radiance value (L Detector max ) of an array of light detectors of the second sensor; 
 determining, based on L Detector max , the maximum irradiance value (E Detector max ) of an array of light detectors of the second sensor. 
 
     
     
       15. The imaging system of  claim 14 , wherein the dynamic link is a proportion between E Sun obs  and E Detector max . 
     
     
       16. The imaging system of  claim 15 , wherein the proportion is applied as a scale to a nominal exposure time of the second sensor. 
     
     
       17. The imaging system of  claim 15 , wherein the dynamic link includes a factor. 
     
     
       18. The imaging system of  claim 17 , wherein the factor is maximum reflectivity of a target (ρ Max target ). 
     
     
       19. The imaging system of  claim 11 , wherein the imaging system is coupled with an unmanned aircraft system (UAS). 
     
     
       20. The imaging system of  claim 19 , wherein the first sensor is an upwards looking sensor on the UAS and the second sensor is a downwards looking sensor on the UAS.